Containers having a reducible volume may e.g. be a rigid outer container with an inner container or inner pouch consisting of a soft material, which after part of the flowable material has been discharged contracts each time accordingly, with pressure compensating openings being provided in the outer container for pressure compensation between the rigid outer container and the inner container. The container, however, may also be single-walled and e.g. have the shape of a tube which is gradually compressed for discharging the material. As further examples of a container having a reducible volume, reference is herewith made to bellows-type containers which gradually collapse in proportion to the discharge of the flowable material, and to syringes whose volume can be reduced by advancing a syringe plunger. It goes without saying that the above enumeration is only by way of example.
The container, however, need not be of a reducible volume. Compensation may also be achieved through inflowing air flowing through a filter (sterile filter).
The flowable material may be a liquid, or it may be a cream, gel, ointment, or another substance, optionally of a high viscosity.
The one-way valve of the above-considered type is meant to discharge the flowable contents of the container in individual partial amounts or doses and, depending on the application, the flowable contents may be discharged in doses, distributed over a prolonged period of time.
When many types of flowable materials are discharged, it is important that the material remaining in the container should not be impaired by the ingress of foreign matter, be it microorganisms or inorganic or organic impurities. Above all in pharmaceutical, but also e.g. in cosmetic flowable materials, this determines the quality, but is e.g. also applicable to substances to be counted among foodstuff. That is why the material volume discharged from the container must not be compensated by air entering into the container if a situation is to be prevented where bacteria, dust, moisture, etc. get into contact with the remaining contents of the container. That is why, as has been mentioned above, the volume must be reduced in the container in question in proportion to the amount of material discharged. It must above all be ensured that no microorganisms penetrate through the container opening and contaminate the remaining contents of the container.